Gore co-sponsored the legislation that created defensenet, a project that military computers and later grew into the worldwide web.
He was pretty much the "Alpha Geek" in the senate from the early 80's, sponsoring and promoting internet related legislation and helping remove the legal obstacles to make the modern internet possible.
While the claim, "I invented the internet," is exaggeration to the point of hubris, Gore was instrumental in the rapid growth of the information superhighway and with Bill Bradley led the group of technogeeks which became known as the "Atari Democrats."
During an interview with Wolf Blitzer last in March 1999, Gore said, 'During my service in the United States Congress, I took the initiative in creating the internet.'
The claim is essentially true - of course it would have been more precise to say 'funding the creation' rather than 'creating'. In the 1980s DARPA, which is part of the Pentagon and financed the first incarnation of the internet, defunded a number of projects, including civilian use of the internet, which weren't directly related to military applications. Gore played a major role in seeing that the internet project was retained under the National Science Foundation, which created nsfnet. Nsfnet ultimately became the internet we know and love today.
The story that Gore said he 'invented' the internet was created by Dick Armey, a Republican member of Congress. Armey's imaginary wording was then picked up by the media, since what Gore actually said wasn't a good enough story. It was often combined with the stories that Gore claimed to have discovered Love Canal(also phony), or that he said that he had inspired 'Love Story' (yes, phony), to produce the theory that Gore is an obsessive fibber.